Combes Stacey A, Dudley Robert
Department of Organismic and Evolutionary Biology, Concord Field Station, Harvard University, Bedford, MA 01730, USA.
Proc Natl Acad Sci U S A. 2009 Jun 2;106(22):9105-8. doi: 10.1073/pnas.0902186106. Epub 2009 May 20.
Environmental turbulence is ubiquitous in natural habitats, but its effect on flying animals remains unknown because most flight studies are performed in still air or artificially smooth flow. Here we show that variability in external airflow limits maximum flight speed in wild orchid bees by causing severe instabilities. Bees flying in front of an outdoor, turbulent air jet become increasingly unstable about their roll axis as airspeed and flow variability increase. Bees extend their hindlegs ventrally at higher speeds, improving roll stability but also increasing body drag and associated power requirements by 30%. Despite the energetic cost, we observed this stability-enhancing behavior in 10 euglossine species from 3 different genera, spanning an order of magnitude in body size. A field experiment in which we altered the level of turbulence demonstrates that flight instability and maximum flight speed are directly related to flow variability. The effect of environmental turbulence on flight stability is thus an important and previously unrecognized determinant of flight performance.
环境湍流在自然栖息地中无处不在，但其对飞行动物的影响仍不为人知，因为大多数飞行研究都是在静止空气中或人工平滑气流中进行的。在此，我们表明外部气流的变化会导致严重的不稳定，从而限制野生兰花蜂的最大飞行速度。在室外湍流空气射流前飞行的蜜蜂，随着空速和气流变化的增加，其横滚轴变得越来越不稳定。蜜蜂以更高的速度向腹侧伸展其后腿，这提高了横滚稳定性，但也增加了身体阻力以及相关的功率需求30%。尽管存在能量成本，但我们在来自3个不同属的10种 Euglossine 蜜蜂中观察到了这种增强稳定性的行为，其体型跨度达一个数量级。我们改变湍流水平的一项野外实验表明，飞行不稳定性和最大飞行速度与气流变化直接相关。因此，环境湍流对飞行稳定性的影响是飞行性能的一个重要且此前未被认识到的决定因素。
